This invention relates to a cap equipped with a mechanism for preventing ink from flowing over the tip of writing equipment such as a pen containing low viscosity liquid ink, and more particularly to a cap effective for writing equipment storing free ink in the body.
A volatile solvent such as water and ethanol is used for low viscosity liquid ink as a main solvent and accordingly caps for writing equipment, e.g. pens containing the liquid ink are so framed as to keep airtight the thin pointed pieces of the pens when they are mounted thereon to prevent the ink from drying. In this sort of pens with caps mounted thereon, the air inside the caps is compressed and caused to flow into the trunks of the pen bodies. In consequence, the pressure in the bodies becomes higher than the atmospheric pressure.
FIG. 12 shows the method of measuring pressure changes in the trunks of the pen bodies. In FIG. 12, a U-shaped tube is filled with water and one end of the tube communicates with the trunk of a pen body, the other end being open. The difference between the water levels is measured while a cap is mounted thereon.
In the case of a conventional cap, the internal pressure of the cap mounted on a pen is seen to increase substantially according to the measurement.
Problems inherent in the conventional cap include often soiling hands, writing paper and clothes because the compressed air contained in the trunk of the pen body expands when the cap is detached from the pen and forces the ink to spout out of the air vent provided at the tip of the pen or close thereto. Such a phenomenon as exemplified above is often the case with writing equipment storing free ink in the trunks of the bodies.